This invention relates to a process for forming a heater chip module adapted to be secured to an ink-filled container.
Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink-filled chamber to expel a droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber on a heater chip near a discharge nozzle. A plurality of chambers, each provided with a single heating element, are provided in the printer""s printhead. The printhead typically comprises the heater chip and a nozzle plate having a plurality of the discharge nozzles formed therein. The printhead forms part of an ink jet print cartridge which also comprises an ink-filled container.
A plurality of dots comprising a swath of printed data are printed as the ink jet print cartridge makes a single scan across a print medium, such as a sheet of paper. The data swath has a given length and width. The length of the data swath, which extends transversely to the scan direction, is determined by the size of the heater chip.
Printer manufacturers are constantly searching for techniques which may be used to improve printing speed. One possible solution involves using larger heater chips. Larger heater chips, however, are costly to manufacture. Heater chips are typically formed on a silicon wafer having a generally circular shape. As the normally rectangular heater chips get larger, less of the silicon wafer can be utilized in making heater chips. Further, as heater chip size increases, the likelihood that a chip will have a defective heating element, conductor or other element formed thereon also increases. Thus, manufacturing yields decrease as heater chip size increases.
Accordingly, there is a need for an improved printhead or printhead assembly which allows for increased printing speed yet is capable of being manufactured in an economical manner.
In accordance with the present invention, a process is provided for forming a heater chip module comprising a carrier adapted to be secured to an ink-filled container, at least one heater chip having a base coupled to the carrier, and at least one nozzle plate coupled to the heater chip. The carrier includes a support substrate having at least one passage which defines a path for ink to travel from the container to the heater chip. The heater chip is secured at its base to a portion of the support substrate. A flexible circuit is coupled to the heater chip module such as by TAB bonding or wire bonding.
Two or more heater chips, positioned end to end, side by side or at an angle to one another, may be secured to a single support substrate.
Each of two or more heater chips coupled to a single support substrate may be dedicated to a different color. For example, three heater chips positioned side by side may be coupled to a single support substrate, wherein each heater chip receives ink of one of the three primary colors.
At least the portion of the support substrate is formed from a material having substantially the same coefficient of thermal expansion as the heater chip base. Thus, the heater chip base and the support substrate portion expand and contract at essentially the same rate. This is advantageous for a number of reasons. First, it is less likely that bonding material joining the heater chip to the carrier will fail. Further, if two or more heater chips are secured to the carrier, accuracy of dot placement is increased as the location of the heater chips relative to the paper is less likely to vary. It is also preferred that the support substrate portion be formed from a material having a thermal conductivity which is substantially the same as or greater than the thermal conductivity of the material from which the heater chip base is formed. Hence, the carrier provides a dissipation path for heat generated by the heater chip. Consequently, heat build up in the heater chip, which might occur if the thermal conductivity of the support substrate portion is less than that of the heater chip base, is avoided.